1. Field
The present disclosure relates generally to acoustic systems and, in particular, to acoustic ranging systems. Still more particularly, the present disclosure relates to a method and apparatus for identifying a distance to a sound source using passive acoustic sensors.
2. Background
In operating unmanned aerial vehicles, sensor systems are used to navigate the unmanned aerial vehicles during flight. These sensor systems may be used by an unmanned aerial vehicle to sense and avoid objects along the flight path of the unmanned aerial vehicle. These objects may be, for example, other aircraft, structures, landmarks, terrain, or some other type of object. To sense these objects, the sensor system may be used to detect the distance of an object from the unmanned aerial vehicle at a point in time.
Some sensor systems may include different types of sensors. Active sensor systems use actively transmitted signals to detect objects. The unmanned aerial vehicle may use an active sensor system such as a radar system. A radar system may use a pulse of electromagnetic radiation to identify a direction and distance of an object from the unmanned aerial vehicle. The distance is determined by the length of time it takes the pulse to return from the object.
This type of sensor system, however, may be undesirable for use in an unmanned aerial vehicle. For example, with a radar system, the emission of electromagnetic radiation makes it easier to identify a presence of the unmanned aerial vehicle. Currently, an unmanned aerial vehicle using a radar system may be detected by undesired parties such as a hostile aircraft or a ground missile station. For example, a hostile aircraft or a ground missile station may identify the presence of the unmanned aerial vehicle by detecting the pulse of electromagnetic radiation emitted by the radar system in the unmanned aerial vehicle. This detection of the unmanned aerial vehicle may be undesirable when the unmanned aerial vehicle is used in a surveillance mission over hostile territories.
Further, a radar system may include more components than desired. For example, the components in a radar system may be larger in size and heavier in weight than desired for an unmanned aerial vehicle. Additionally, a radar system may take up more space than desired in an unmanned aerial vehicle. Further, a radar system may use more energy than desired when transmitting electromagnetic radiation.
Therefore, it would be desirable to have a method and apparatus that takes into account at least one of the issues discussed above as well as possibly other issues.